1. Field of the Invention
The present invention relates to a topical negative pressure (TNP) assisted wound dressing particularly, though not exclusively, for the treatment of wounds of relatively low area and/or relatively low volume.
The subject of this invention is an apparatus for the management of small to medium sized wounds that utilises a vacuum source but manages wound exudate in a traditional manner by utilising an absorbent self-cohesive material in the wound cavity. No fluid is exported from the locality of the wound cavity other than by local evaporation. In this manner, an extremely portable system, of minimal inconvenience to the wearer, can be generated.
2. Background to the Invention
TNP therapy has enjoyed relatively recent commercial success. WO9605873 and its family members describes a portable TNP therapy apparatus. The apparatus described mechanically supports tissue in the vicinity of the wound site and tissue mechanics and the rate of exudation from such sites requires a system such as that described in WO9605873 or as described in patents such as GB2378392 and WO2005/082435 which have remote waste receptacles to which wound exudate fluid is aspirated in order to cope with the volume of fluids generated in a relatively short time, less than that period in which a dressing would normally be left in place. However, for wounds of surface area below approximately 200 cm2 or internal volumes below about 1000 cm3 these solutions may not be the most appropriate since exudate volumes and exudate rates from these wounds may be managed by more traditional wound dressings, requiring dressing change every 3-7 days. The relatively small dimensions of such wounds do not make them attractive for the traditional TNP therapies disclosed in the prior art; these devices typically including a remote vacuum source, fluid transfer lumen and remote fluid collection receptacle, control and power source and are of dimensions and weight exceeding those convenient or discrete for the patient to carry.
The general principles of TNP apparatus described in the prior art comprise a fluid-permeable wound cavity filling element, a dressing for covering the wound and providing a reasonably air-tight seal around the wound, a drainage tube connecting the wound site and cavity filling element to the vacuum source via a fluid collection canister. The precise nature of the wound filling element has been the subject of much invention in this field. The mode of action of the apparatus is the application of negative pressure to the wound cavity, causing compression of the wound cavity filler and expansion of the surrounding tissue into the wound cavity. Wound exudate is drawn from the surrounding tissue, through the still porous cavity filler, along the drainage tube and into the remote collection receptacle. An important feature of the prior art is the ability of the wound cavity filler to remain sufficiently porous, when compressed under negative pressure, to allow fluid transport from the tissue to the drainage or aspirant tube. Porosity can be facilitated at the molecular level, for example in a hydrogel, or at the microscopic level, for example in a hydrocellular foam. To facilitate fluid flow, a hydrophobic filling has been deemed particularly desirable by workers in the field and absorbent fillers as being particularly undesirable due to their hindering fluid transport.
In contrast to the principles of TNP therapy, the general principle of traditional wound dressings is the localisation of wound exudate at the locality of the wound, either within the wound cavity or in close proximity to the surface. For this purpose, extremely absorbent materials are desirable that retard the free flow of fluid, preferably absorbing the fluid and localising it. Aquacel (trade mark) made by ConvaTec Ltd is an example of a non-woven dressing that absorbs substantial quantities of fluid and effectively locks it in the dressing. Allevyn (trade mark) made by Smith & Nephew Ltd is an example of a foam dressing that absorbs substantial quantities of fluid while allowing rapid transpiration through a high moisture vapour permeable top-film.
In summary, the prior art deals exclusively with vacuum assisted fluid transport away from the site of the wound. A very broad range of wound cavity filling and contacting elements have been described and exemplified in the prior art, including materials commonly used in traditional wound care dressings. Without exception in these cases, the cavity filling and wound contacting elements act as a conduit for the transport of fluid from the wound per se to a remote collection canister via an aspirant tube connected to a vacuum source.